not really that big on what's the best equipment, but if you can.... somehow fit a refugium and a skimmer in there.
Refugium is probably one of the better filtrations to have... low maintenance and feeds off the bad bacteria.
Skimmer,.... its not essential but definitely worth it. try to look for one minimally for your tank size and nothing less... or if your thinking of an upgrade on the tank or wanting corals then try to look at one for a bit more larger tank than the 55g
For a return pump, minimally look for at least 10x your water capacity, would be better if you look into 15x though.
Not the best info lol but hope it helps